Patent GB-727976-A (GB)
Title: Improvements in and relating to pilot-operated directional control valves
Inventor: TOWLER JOHN MAURICE
IPC: F15B13/04
Filed: 1951-12-11
Abstract: 727,976. Hydraulic presses; valves. ELECTRAULIC PRESSES, Ltd. Dec. 5, 1952 [Dec. 11, 1951], No. 28971/51. Classes 69 (2) and 135. A hydraulic control valve for directing both primary and pilot pressure liquids to and from apparatus in a hydraulic system comprises a valve plunger movable in one or in both directions by pilot pressure liquid under the control of a further valve in relation to inlet and outlet ports in the valve casing through which the primary and pilot pressure liquids flow. As shown in Fig. 1, Provisional Specification, the valve V2 comprises a casing 1 having ports 31, 32, connected to a manually-actuated further valve V3, Fig. 5, Complete Specification, to which pilot pressure liquid is supplied, ports 14, 15, through which pilot pressure liquid is directed to close a normally open pump by-pass valve V4, a primary pressure supply port 12 connected through the valve V4 to a pump P, exhaust ports 11, 13, a motor port 16, through which primary pressure liquid passes to and from the undersides of approach rams b and from the main ram a of a single up-stroking press and a port 17 through which primary pressure liquid passes to and from the upper sides of rams b. The valve spool 2 loaded by centralizing springs 33, 34 is provided at one end with axial and radial bores 25, 26 and secured to a cylinder 4 slidably mounting a plunger 41 engageable by an adjustable stop 44. The hydraulic system for controlling the press also includes a valve V7 operated by the pressure in the approach cylinders to control the flow of pilot pressure liquid to and from a valve V6 controlling the admission of primary pressure liquid to the main press cylinder a after the work has been contacted, a prefill and exhaust valve V1 by means of which liquid is allowed to rapidly flow between the main press cylinder and a supply tank, a relief valve V8 and non- return check valves V5A, V5B. With the press inoperative, the valves V2, V3 and V7 are in their neutral inoperative positions, the valve V4 open to connect the pump to sump and the valve V6 closed. To up-stroke the ram a, the valve V3 is operated to connect pilot pressure liquid to the ports 31, 3c of the valves V2, V7 respectively and to connect the port 32 of the valve V2 to exhaust. The spool 2 then moves rightwardly to connect ports 12 and 16, ports 13 and 17 and just before its maximum stroke opens the port 14 so that pilot pressure liquid is supplied to act on a piston g of the valve V4 to close this valve. Primary pressure liquid then passes through port 1d to the valve V6 and through the check valve V5A to the valve V2 when it is directed through the ports 12, 16 to the undersides of the rams b, the upper sides of these rams being open to exhaust through the ports 17, 13. The rams b are then raised together with the ram a which is supplied with pressure liquid through the valve m of the prefill and exhaust valve V1, this valve opening due to the pressure head of liquid in a supply tank (not shown) to quickly fill the main ram cylinder. When the rams b reach the ends of their strokes, pressure builds up in their cylinders and this pressure acts on the underside of a valve piston j of the valve V7 to connect the pilot pressure liquid to the underside of a piston k of the valve V6 which valve now opens to connect full pump pressure directly to the main ram cylinder to complete the pressing operation. To release the pressure in the main ram cylinder and from the undersides of the rams b to down-stroke the press, the valve V3 is now operated to supply pilot pressure liquid to the port 32 of the valve V2 and exhaust pilot pressure liquid therefrom through its port 31, and the valve V3. The spool 2 together with the cylinder 4 and plunger 41 now move leftwardly until the plunger 41 is arrested by the stop 44. In this position restricted exhaust takes place through the ports 16, 11, from the main ram cylinder through the check valve V5B, and from beneath the rams b, and the supply of pilot pressure liquid to the valve V4 is interrupted to allow this valve to open to unload the pump. The pressure of the exhausting liquid acts on the plunger 41 to hold its head in contact with the cylinder 4 until the pressure has been sufficiently reduced whence the plunger will be unseated and the spool will move to its extreme left position to fully open the main and approach ram cylinders to exhaust and connect the valve V4 through the port 15 to the supply of pilot pressure liquid to again load -the pump. The reduced pressure beneath the rams b reduces the pressure beneath the valve piston j of the valve V7 allowing this valve to cut off the supply of pilot pressure liquid to the valve V6 which closes to disconnect the main ram cylinder from the pump. With the pump again loaded primary pressure liquid is directed through ports 12, 17 to the upper faces of the rams b to move these rams downwards and at the same time acts on a spring- loaded plunger l in the valve V1 to unseat its valve m to exhaust liquid rapidly from the main ram cylinder back to the supply tank. If desired, a cylinder 4 and plunger 41 may also be fitted to the right-hand end of the spool 2 with an associated adjustable stop 44 and bores 25, 26 so that when the valve is used to operate a double-acting press, the exhaust of pressure liquid is initially controlled from both ends of the press. The control valve V2 may be mounted on a manifold 5, Fig. 2, so that several such control valves controlling individual presses may be mounted side by side and be supplied by a common pump. Each valve being connected to a common pump supply duct 52 through its individual non-return valve 59, to common exhaust ducts 51, 53 and individual press ports 54, 55.